Occasional Pot Use May Harm Young People's Brains

Published 04/18 2014 12:11PM

Updated 05/23 2014 10:20AM

The national mood has shifted dramatically in the last few years concerning the recreational and medical use of marijuana and many people are convinced that an occasional joint isn't harmful and should be legalized.

For the young people - and their parents - who think that smoking pot in moderation isn't harmful, a new study says you may want to review what scientists have discovered before you take another toke.

A study released this week by researchers from Northwestern University's Feinberg School of Medicine and Harvard Medical School has found that 18- to 25-year-olds who smoke marijuana only recreationally showed significant abnormalities in the brain.

"There is this general perspective out there that using marijuana recreationally is not a problem — that it is a safe drug," says Anne Blood, an assistant professor at Harvard Medical School and the co-senior author of the study, which is being published in the Journal of Neuroscience. "We are seeing that this is not the case."

For decades, people who enjoy smoking pot have cited that it is less harmful than alcohol, tobacco and even sugar. The 1936 exploitation movie "Reefer Madness" and exaggerated warnings from public service announcements have probably done more to encourage marijuana use because they were either ridiculous or emotionally manipulative.

Now that legalization of marijuana use is on the front burner, science is interested is finding out if the drug is or is not harmful to those who smoke it.

Scientists in the new Northwestern-Harvard study used three different methods of neuroimaging analysis to examine the brains of 40 young adult students from Boston-area colleges: 20 who smoked marijuana casually — four times a week on average — and 20 who didn't use pot at all.

Each group consisted of nine males and 11 females. The marijuana smokers underwent a psychiatric interview to confirm that they were not heavy or dependent marijuana users.

"We looked specifically at people who have no adverse impacts from marijuana — no problems with work, school, the law, relationships, no addiction issues," says Hans Breiter, a professor of psychiatry and behavioral sciences at the Feinberg School and co–senior author of the study.

The scientists examined two key parts of the brain — the nucleus accumbens and the amygdala, which together help control whether people judge things to be rewarding or aversive and, in turn, whether they experience pleasure or pain from them. It is the development of these regions of the brain, Breiter says, that allows young people to expand their horizons, helping them appreciate and enjoy new foods, music, books and relationships.

"This is a part of the brain that you absolutely never ever want to touch," Breiter asserts. "I don't want to say that these are magical parts of the brain — they are all important. But these are fundamental in terms of what people find pleasurable in the world and assessing that against the bad things."

Breiter and his colleagues found that among all 20 casual marijuana smokers in their study — even the seven who smoked just one joint per week — the nucleus accumbens and amygdala showed changes in density, volume and shape. The scientists also discovered that the more pot the young people smoked, the greater the abnormalities.

Researchers noted that the sample size for the study was small and their findings were preliminary. More research is needed, they say, to understand the relationship between the changes to the brain they found and the impact on the day-to-day lives of young people who smoke marijuana casually.

"The next important step is to investigate how structural abnormalities relate to functional outcomes," says Jodi Gilman, an instructor at Harvard Medical School who collaborated on the study.

This is especially important, she and her colleagues add, in light of the growing push to legalize recreational marijuana use across America. "People think a little marijuana shouldn't cause a problem if someone is doing O.K. with work or school," Breiter says. "Our data directly says this is not so."

More information is needed as we move into a future where marijuana use is becoming more and more accepted. Does smoking pot have negative long-term effects on the brain, particularly brains that are still developing?

The time has come to put aside our biases, either pro or con, and the silly reefer madness movies and take a serious approach and thoughtful look at the science of drug use and its effect on the most important organ in our body, the brain.